Soft chemistry synthesis and characterization of layered Li1-xNi1-yCoyO2-δ (0 ≤ x ≤ 1 and 0 ≤ y ≤ 1)

Li1-xNi1-yCOyO2-delta oxides have been synthesized for 0 less than or equal to x less than or equal to 1 and 0 less than or equal to y less than or equal to 1 by chemically extracting lithium at ambient temperature from LiNi1-yCOyO2 with an oxidizing agent NO2-PF6 in acetonitrile medium. The samples have been characterized by X-ray diffraction, wet-chemical analyses to determine lithium and oxygen contents, and infrared spectroscopy. While the nickel-rich end members Ni1-yCOyO2-delta have the O3 structure similar to the initial LiNiO2, but with smaller lattice parameters, the cobalt-rich end members Ni1-yCOyO2-delta consist of a mixture of P3 and O1 phases that are formed from the initial O3 structure of LiCoO2 by a sliding of the oxide-ion layers. The nickel-rich phases Li1-xNi1-yCoyO2-delta have an oxygen content close to 2 with a negligible amount of oxygen vacancies, while the cobalt-rich phases have considerable amount of oxygen vacancies (delta = 0.33 in CoO2-delta). Fourier transform infrared spectroscopy indicates a semiconductor to metal transition in Li1-xCoO2-delta for (1- x) < 0.77. On the other hand, Li1-xNi1-yCoyO2-delta oxides with 0 less than or equal to y less than or equal to 0.5 remain as semiconductors for the entire 0 less than or equal to (1 - x) less than or equal to 1. The differences in oxygen loss behavior and electrical conduction are explained on the basis of qualitative band diagrams.